1. Field of the invention
This invention relates to a toner for developing an electrostatic image, used in electrophotography, electrostatic recording and magnetic recording.
2. Related Background Art
A number of methods have been known for electrophotography as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publications No. 42-23910 and No. 43-24748 and so forth. In general, copies are obtained by forming an electrostatic latent image on a photosensitive member by utilizing a photoconductive material and by various means, subsequently developing the latent image with a toner, and transferring the toner image to a recording medium such as paper if necessary, followed by fixing with heat, pressure, heat-and-pressure, or solvent vapor. The toner not transferred and remaining on the photosensitive member is cleaned by various means, and then the above process is repeated.
In recent years, such copying apparatuses have been used not only as office copying machines to merely make copies of originals but have also been used as printers for output means of computers or in the field of personal use.
Under such circumstances, the downsizing and weight reduction of the apparatus are eagerly sought as well as the higher speed and higher reliability. Thus, the constitution elements of the machines now become simpler in various points. As a result, higher performance is required for the toner, and it is now impossible to improve machines without accomplishing the improvement of the toner performance.
It is known to incorporate wax in the toner as a fixing auxiliary component. For example, such techniques are disclosed in Japanese Patent Applications Laid-open No. 52-3304, No. 52-3305 and No. 57-52574.
Techniques for incorporating waxes are also disclosed in Japanese Patent Applications Laid-open No. 3-50559, No. 2-79860, No. 1-109359, No. 62-74166, No. 61-273554, No. 61-94062, No. 61-138259, No. 60-252361, No. 60-252360 and No. 60-217366.
Waxes are used to improve anti-offset properties of toners in low- and high-temperature fixing or to improve fixing performance in low-temperature fixing.
It is difficult, however, to satisfy both low-temperature fixability and anti-blocking property. In printers or copying machines using electrophotographic techniques, corona dischargers have been commonly used as a means for uniformly charging the surface of a photosensitive member (an electrostatic image bearing member) or as a means for transferring a toner image to the surface of the photosensitive member. However, a direct charging and transfer method has been developed in which voltage is externally applied to the charging means while the charging member is in contact with, or pressed against, the surface of the photosensitive member directly or through a recording medium. This method is now in practical use.
Such a method is disclosed, for example, in Japanese Patent Applications Laid-open No. 63-149669 and No. 2-123385. These are concerned with contact charging or contact transfer, where a conductive elastic roller is brought into contact with an electrostatic image bearing member to uniformly charge the electrostatic image bearing member by applying a voltage to the conductive roller, the image bearing member is then subjected to exposure and development to obtain a toner image, and thereafter, another conductive elastic roller to which a voltage has been applied is pressed against the electrostatic image bearing member interposing a transfer medium between them to transfer the toner image formed on the electrostatic image bearing member to the transfer medium, followed by fixing to obtain a copied image.
In such a process, the toner is pressed to the photosensitive member by the charging members, and hence the toner tends to melt-adhere to the photosensitive member. This tendency increases when a wax is used to improve fixing performance.